1. Field of the Invention
The present invention relates generally to the field of electric motors. More particularly, the invention relates to a novel technique for establishing the efficiency of a motor under either balanced or unbalanced operating conditions.
2. Description of the Related Art
A wide variety of induction motors are available and are currently in use throughout a range of industrial applications. In general, such motors include a stator provided in a motor housing and a rotor surrounded at least partially by the stator and supported for rotation within the housing. The stator and rotor may be mechanically and electrically configured in a variety of manners depending upon a number of factors, including: the application, the power available to drive the motor, and so forth. In general, however, electric power is applied to the stator to produce a rotating magnetic field to drive the rotor in rotation. Mechanical power is transmitted from the motor via an output shaft coupled to the rotor.
In many industrial applications, induction motors are powered by three-phase alternating current. When the three-phase alternating voltage is balanced, the three phases have approximately the same maximum values for the voltage and current. However, the three-phase alternating voltage supplied to a motor may be unbalanced. An unbalanced operating condition may be caused by single-phase loads connected one or more of the three phases. When the three-phase alternating current is unbalanced, the three phases will not have the same maximum values of voltage and current. This unbalanced condition causes additional losses in the motor. As a result, a motor operated in an unbalanced condition is not as efficient as a motor operated in a balanced condition.
Typically, it is desired to know the efficiency at which a motor is being operated. However, there is no current technique that enables the efficiency of a motor to be established when the motor is operated in an unbalanced condition. A need exists for a technique to enable the efficiency of a motor operated in an unbalanced condition to be established